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  #1  
Old 08-28-2002, 01:58 PM
Lee Derby
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Tachometer anomalies

I have an 83 300D Turbo. The Tachometer is dead except once in a while it moves at an erratic rate usually between shifts or at higher speeds on the highway. I tried the cigarette butt under the amplifier cap, then resoldered all the connections on the circuit board (took a lot of time to remove all the silicon potting). It still does the same thing. I can see the pick-up for the amp going to the front of the engine but haven't been able to see where it goes. Does anyone think the pick-up might have come loose? Any recomendations on how to check the pick-up for looseness? Thanks in advance.
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  #2  
Old 08-28-2002, 11:05 PM
RSH RSH is offline
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Tachometer anomalies

When I first picked up my 83 300SD the tach would occasionaly work in a eratic sense at best, I looked up all the "tricks" on the internet to no avail, futher investigation revealed that the tach sensor mount was bent about 45' and no way was the magnetic pickup going to work with the sensor being that far off, I think someone must have used a pry bar to adjust a belt and thats how it got bent, I straightened it out, started the car, still no tach, I removed the sensor and its pickup point was caked with crud, cleaned the sensor up, reinstalled it, started the car and the tach worked 90% of the time, did a different mod under the tach amp/diagnostic cap, I cut out a circular section of 1/8" fiberglass the same diameter as the inside of the tach amp/diagnostic cap to put even pressure on the pins and the tach has operated 100% ever since.
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  #3  
Old 08-29-2002, 03:21 PM
Lee Derby
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Thanks a lot RSH. I think that is my problem too. How did you get access to the tach sensor and bracket? It looks like I have to remove a lot of stuff to even see it. Radiator, belts, vacuum pump, etc. I only bought mine in May of this year and the tach never did work right. Is the tach pick-up on the SD on the front of the engine or on the rear? I too read the threads on tach problems. But this is the first I've seen on this problem.
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  #4  
Old 08-30-2002, 01:54 AM
RSH RSH is offline
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Tachometer anomalies

The tach sensor on my 83 300SD is located at the front of the engine just right of center and over the the top of the crank pulley, it's easy to see, or you could follow the the sensor wire (mine has white insulation) from the tach amp/diagnostic cap to where the sensor is.

Last edited by RSH; 08-30-2002 at 02:29 AM.
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  #5  
Old 09-01-2002, 12:04 PM
Lee Derby
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Thanks again RSH. I will look as soon as I get a chance. This is not a high priority item but it bugs me that it doesn't work. Because of guys like you a lot of us surf these forums for ideas that we might use in the future too. It's really amazing how many people are ready to help on a moments notice.
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  #6  
Old 09-20-2002, 10:52 PM
Lee Derby
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Finally had a chance to look at my tach pick-up. It's just as you said. Thanks. I have one more question, What is the gap between the post and pick-up supposed to be? Or at least an approximation. I said I finally had a chance to look at the tach set up because I was replacing a half-axle that gave me weird symptoms.(writing separate thread on that one). Thanks again RSH
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  #7  
Old 11-10-2009, 06:54 AM
Yashpal Amarsingh
 
Join Date: Apr 2009
Location: INDIA
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Quote:
Originally Posted by Lee Derby View Post
Finally had a chance to look at my tach pick-up. It's just as you said. Thanks. I have one more question, What is the gap between the post and pick-up supposed to be? Or at least an approximation. I said I finally had a chance to look at the tach set up because I was replacing a half-axle that gave me weird symptoms.(writing separate thread on that one). Thanks again RSH
Sir,
Did you manage to get the information on the gap between the post and the pickup. I too need this info for my 1980 300SD Turbo.
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  #8  
Old 11-10-2009, 11:11 AM
toomany MBZ's Avatar
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Location: central Va
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That would be very, very close. I've seen pick ups scored by the pin.
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83 SD

84 CD
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  #9  
Old 11-11-2009, 02:11 AM
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Originally Posted by Yashpali View Post
Sir,
Did you manage to get the information on the gap between the post and the pickup. I too need this info for my 1980 300SD Turbo.
LEE DERBY isn`t around any more to answer the question. this thread is from 02.

I have an 85 so my pick up is different.

Charlie
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